criu/pagemap-cache.c

#include <unistd.h>
#include <fcntl.h>

#include "pagemap-cache.h"
#include "compiler.h"
#include "xmalloc.h"
#include "util.h"
#include "log.h"
#include "vma.h"

#undef	LOG_PREFIX
#define LOG_PREFIX "pagemap-cache: "

/* To carry up to 2M of physical memory */
#define PMC_SHIFT		(21)
#define PMC_SIZE		(1ul << PMC_SHIFT)
#define PMC_MASK		(~(PMC_SIZE - 1))
#define PMC_SIZE_GAP		(PMC_SIZE / 4)

#define PAGEMAP_LEN(addr)	(PAGE_PFN(addr) * sizeof(u64))

static inline void pmc_reset(pmc_t *pmc)
{
	memzero(pmc, sizeof(*pmc));
	pmc->fd = -1;
}

static inline void pmc_zap(pmc_t *pmc)
{
	pmc->start = pmc->end = 0;
}

int pmc_init(pmc_t *pmc, pid_t pid, struct list_head *vma_head, size_t size)
{
	size_t map_size = max(size, (size_t)PMC_SIZE);
	pmc_reset(pmc);

	BUG_ON(!vma_head);

	pmc->pid	= pid;
	pmc->fd		= open_proc(pid, "pagemap");
	pmc->map_len	= PAGEMAP_LEN(map_size);
	pmc->map	= xmalloc(pmc->map_len);
	pmc->vma_head	= vma_head;

	if (!pmc->map || pmc->fd < 0) {
		pr_err("Failed to init pagemap for %d\n", pid);
		pmc_fini(pmc);
		return -1;
	}

	pr_debug("created for pid %d (takes %zu bytes)\n", pid, pmc->map_len);

	return 0;
}

static inline u64 *__pmc_get_map(pmc_t *pmc, unsigned long addr)
{
	return &pmc->map[PAGE_PFN(addr - pmc->start)];
}

static int pmc_fill_cache(pmc_t *pmc, struct vma_area *vma)
{
	unsigned long low = vma->e->start & PMC_MASK;
	unsigned long high = low + PMC_SIZE;
	size_t len = vma_area_len(vma);
	size_t size_map;

	if (high > TASK_SIZE)
		high = TASK_SIZE;

	pmc->start = vma->e->start;
	pmc->end = vma->e->end;

	pr_debug("filling VMA %lx-%lx (%zuK) [l:%lx h:%lx]\n",
		 (long)vma->e->start, (long)vma->e->end, len >> 10, low, high);

	/*
	 * If we meet a small VMA, lets try to fit 2M cache
	 * window at least 75% full, otherwise left as a plain
	 * "one vma at a time" read. Note the VMAs in cache must
	 * fit in solid manner, iow -- either the whole vma fits
	 * the cache window, either plain read is used.
	 *
	 * The benefit (apart redusing the number of read() calls)
	 * is to walk page tables less.
	 */
	if (len < PMC_SIZE && (vma->e->start - low) < PMC_SIZE_GAP) {
		size_t size_cov = len;
		size_t nr_vmas = 1;

		pr_debug("\t%16lx-%-16lx nr:%-5zu cov:%zu\n",
			 (long)vma->e->start, (long)vma->e->end, nr_vmas, size_cov);

		list_for_each_entry_continue(vma, pmc->vma_head, list) {
			if (vma->e->start > high || vma->e->end > high)
				break;

			BUG_ON(vma->e->start < low);
			size_cov += vma_area_len(vma);
			nr_vmas++;

			pr_debug("\t%16lx-%-16lx nr:%-5zu cov:%zu\n",
				 (long)vma->e->start, (long)vma->e->end, nr_vmas, size_cov);
		}

		if (nr_vmas > 1) {
			/*
			 * Note we don't touch low bound since it's set
			 * to first VMA start already and not updating it
			 * allows us to save a couple of code bytes.
			 */
			pmc->end = high;
			pr_debug("\tcache  mode [l:%lx h:%lx]\n", pmc->start, pmc->end);
		} else
			pr_debug("\tsimple mode [l:%lx h:%lx]\n", pmc->start, pmc->end);
	}

	size_map = PAGEMAP_LEN(pmc->end - pmc->start);
	BUG_ON(pmc->map_len < size_map);

	if (pread(pmc->fd, pmc->map, size_map, PAGEMAP_PFN_OFF(pmc->start)) != size_map) {
		pmc_zap(pmc);
		pr_perror("Can't read %d's pagemap file", pmc->pid);
		return -1;
	}

	return 0;
}

u64 *pmc_get_map(pmc_t *pmc, struct vma_area *vma)
{
	/* Hit */
	if (likely(pmc->start <= vma->e->start && pmc->end >= vma->e->end))
		return __pmc_get_map(pmc, vma->e->start);

	/* Miss, refill the cache */
	if (pmc_fill_cache(pmc, vma)) {
		pr_err("Failed to fill cache for %d (%lx-%lx)\n",
		       pmc->pid, (long)vma->e->start, (long)vma->e->end);
		return NULL;
	}

	/* Hit for sure */
	return __pmc_get_map(pmc, vma->e->start);
}

void pmc_fini(pmc_t *pmc)
{
	close_safe(&pmc->fd);
	xfree(pmc->map);
	pmc_reset(pmc);
}